1. Field of the Invention
The present invention relates to a self-diagnostic system for determining maintenance conditions of lubricants in oil-utilizing machines operating under intermittent loads. More particularly, the present invention relates to a system and method for determining the condition of oil in an internal combustion engine, transmission, or the like, in order to optimize oil maintenance intervals.
2. State of the Art
Lubricating oils are typically comprised of high molecular-weight products of the petroleum distillation process. The base constituents of these oils are typically hydrocarbon chains having anywhere from 16 to 30 carbon atoms, and a boiling point higher than 350.degree. C. Undesired constituents such as tars, asphalts, greases, and paraffin waxes are preferably removed during the refining process, and certain additives such as thickening agents, detergents, and anti-oxidants may be added to impart desired properties to the oil.
As oil is used in the high temperature, high stress environment of an internal combustion engine or other oil-utilizing machine, the base hydrocarbons tend to break down over time. Typically, the relatively long hydrocarbon chains of the base oil break up and degrade into oxidized forms of hydrocarbons such as polyacohols, aldehydes, carboxylic acids, esters, etc., which have inadequate or undesirable properties. When some significant proportion of the base oil has broken down in this way, the oil will no longer protect the machine from damage as desired.
At present, oil changes in internal combustion engines and similar oil-utilizing machines are typically performed according to the mileage or hours of operation of the machine, not according to the directly identified needs given by the chemical state of the lubricating oil. However, it will be appreciated that the miles driven or hours of use do not necessarily indicate the condition of the oil. For example, operation under heavy or rapidly varying loads, or under dusty or hot conditions will tend to cause oil to break down sooner than otherwise. A mileage or time-based schedule is thus only an approximation of the actual needs, based on numerous assumptions. The result is that the lubricating oil may be changed too infrequently, resulting in accumulated damage to the mechanical parts, or it may be changed more often than needed, causing needless maintenance expense and producing excessive waste oil. While one could periodically remove a sample of oil from a vehicle's oil reservoir and have it chemically tested, this is so time consuming, expensive, and inconvenient as to be essentially impractical.
It would be desirable to have a self-diagnostic system that could sense the actual chemical condition of the lubricating oil in intermittently operated machines, and provide an operator or maintenance person with an indication when the oil has reached a certain point of chemical degradation.